In recent years, large-scale integrated circuits (LSIs), each comprising many transistors, many resistors and many similar elements connected, constituting an electric circuit, are incorporated in great numbers in the major components of computers or communication apparatuses.
The performance of an LSI can be enhanced by increasing its integration density, that is, by making its elements smaller. To make the elements smaller it is necessary to employ techniques of forming thin films in grooves having a large aspect ratio.
One of the techniques of forming thin films is the plasma CVD method in which a low-pressure plasma source is used. The plasma CVD method is attracting attention because the gases have long mean free path, providing reactive species which can propagate very linearly. Known as low-pressure plasma sources are EBEP (Electron Beam Excited Plasma), ECR (Electron Cyclotron Resonance) plasma, HELICON plasma and the like.
In the plasma CVD method using a low-pressure plasma source, a voltage is applied to a substrate being processed, so that ions of deposited species are positively drawn from the plasma to the substrate. A thin film 82 having a high directionality can thereby be formed in a groove formed in the substrate and having vertical wall surfaces.
If the groove such a tapered one as is shown in FIG. 6, a thin film 82 will be formed also on the wall surfaces of the groove. In this case, it is difficult to form a film having a high directionality.
As described above, the conventional plasma CVD method using a low-pressure plasma source has the problem that a film will be formed also on the wall surfaces of a tapered groove which has a high aspect ratio and which has tapered wall surfaces.
The present invention has been made in consideration of the above circumstances. Its object is to provide a method of forming a thin film in a groove made in a surface of a substrate 81 being processed, by applying a voltage to the substrate, thereby drawing ions of deposited species from plasma to the substrate, even if the groove is a tapered one having a high aspect ratio.